The present invention relates to a distance measuring device for an automatic focusing camera. More particularly, the invention relates to a distance measuring device for an automatic focusing camera which automatically arranges the lenses thereof into an in focus position in accordance with information data of distance from the camera to an object to be taken as a photograph which data is obtained by emitting a detection beam from a light emitting diode (LED) to the object and detecting an incident point of the light reflected from the object on a light receiving element arranged within the camera. Further, the present invention may advantageously be applied to an automatic focusing camera provided with an alarm device which alarms when the distance to the object is too short to focus the lenses thereof on the object on the basis of the information data of the distance to the object.
Conventionally, a triangulation distance measuring method is known as a means for measuring the distance from the camera to the object. The known distance measurng means comprises an LED which emits a detection light toward the object and a light receiving element which is disposed at a position separated away from the LED by a predetermined reference length so as to receive the light reflected from the object. Such a distance measuring method is utilized for obtaining distance information data for driving an automatic focus adjusting means of the lenses of an automatic focusing camera which is called an AF camera and operates to automatically bring the lenses to an in focus position in accordance with the AF function thereof. Various kind of AF cameras have been developed and widely used.
The conventional AF camera comprises a finder display having an area mark provided thereon for defining an area in which the distance to the object can be measured by the AF function thereof.
Also, as another conventional camera, Japanese Unexamined Pat. Publication No. 60-140306 discloses a wide field camera which makes it possibly to widen the field of the lens of the camera by arranging a plurality of LEDs which are driven to emit light in a predetermined time sequence.
Also, another wide field AF camera which comprises a plurality of LEDs to widen the field of the lens of the camera is disclosed in Japanese Unexamined Pat. Publications Nos. 60-147709, 60-144711 and 60-168111.
Also, Japanese Unexamined Pat. Publication No. 59-198410 discloses an automatic focal length detection device which comprises one LED and two optical systems which have a different optical characteristic with respect to each other for the LED and which is arranged so that the system to be used is changed mechanically in accordance with the distance to the object.
However, in accordance with the above mentioned conventional AF cameras, there is a case in which the distance is mistakenly measured or impossible to measure when the object is positioned at a certain distance from the lens.
In order to solve this problem, the above mentioned arrangement which comprises one LED and two changeable optical systems is proposed in the Japanese Unexamined Pat. Publication No. 59-198410 mentioned above. However, the mechanical means for changing the optical system can not accurately positions the lenses at a predetermined position at the time of changing the system because of mechanically movable members to be driven, which degrades the reliability of measurement and increases the producing cost due to the increase of the number of components to be assembled.
Besides, the above mentioned patent publications do not disclose a technical solution to enlarge the range of measurable distance to the object from the camera.